TABLE OF CONTENTS It is well known that a delta to delta-wye three-winding transformer feeding a 12-pulse converter will eliminate harmonics of order 6 n 1 in the primary current, but just how this is accomplished is not at all obvious, since currents 30 apart certainly do not cancel. If the transformer wye secondary voltage leads the delta secondary voltage by 30 , the following expressions for fundamental currents obtain:
| Secondary | Phase A | Phase B | Phase C |
|---|---|---|---|
| Delta | sin( ?) | sin( ? 120 ) | sin( ? + 120 ) |
| Wye | sin( ? + 30 ) | sin( ? 90 ) | sin( ? + 150 ) |
If the secondaries carry fifth harmonic currents, these currents will multiply the angles of each fundamental by 5, with the following result:
| Delta | sin(5 ?) | sin(5 ? 600 ) | sin(5 ? + 600 ) |
| Wye | sin(5 ? + 150 ) | sin(5 ? ? 450 ) | sin(5 ? + 750 ) |
The these expressions can be rewritten as:
| Delta | sin(5 ?) | sin(5 ? + 120 ) | sin(5 ? ? 120 ) |
| Wye | sin(5 ? + 150 ) | sin(5 ? 90 ) | sin(5 ? + 30 ) |
Harmonic currents in the delta secondary lines will become the same currents in the primary lines. The wye currents, however, will become delta currents in the primary, and the primary line current will be the difference between two wye currents with a ratio of 1/ ?3. The following equations then apply for primary...
